(1) Field of the Invention
The present invention relates to a process for the preparation of an electroconductive polymeric material oriented in a certain direction.
(2) Description of the Related Art
As the semiconductive material, there can be mentioned element semiconductors such as silicon (Si) and germanium (Ge) and compound semiconductors such as gallium arsenide (GaAs) and indium phosphide (InP), and devices such as transistors and IC are fabricated by using these semiconductor materials. Each of these semiconductor materials is an inorganic material.
Polyacetylene (CH).sub.n is an aliphatic unsaturated hydrocarbon having conjugated double bonds in the molecule, and polyacetylene can be rendered electroconductive by adding an impurity such as iodine (I) at a low concentration, and it is known that the electric conduction mechanism of this electroconductive polymeric material is different from that of the conventional inorganic semiconductor (A. J. Epstein, Physical Review Letters, Vol. 50, No. 23, page 1866, 1983).
Since this electroconductive polymeric material can be easily formed into a thin film, the material has attracted attention as a semiconductor device-forming material and investigations have been made into a practical utilization thereof.
A thin film of polyacetylene can be prepared by using a Ziegler-Natta catalyst comprising triethyl aluminum (abbreviated to AlEt) and tetrabutoxy titanium [abbreviated to Ti(OBu).sub.4 ] and introducing acetylene (HC.tbd.HC) gas to a substrate to which the catalyst is applied in the form of a film.
When the so-formed polyacetylene film is observed by a microscope, it is seen that molecule chains and hairy fine fibers (fibrils) grow while randomly crossing one another, to form a film. Polyacetylene has an anisotropy in the direction of electric conduction and is characterized in that the electric resistance is low in the longitudinal direction of the fibril. Nevertheless an unoriented film in which fibrils grow while randomly crossing one another does not show a high conductivity.
For example, a process has been proposed in which polyacetylene is synthesized in the form of a film and the film is patterned by the lithographic technique to form an element comprising an insulating zone and an electroconductive zone (see, for example, Japanese Unexamined Patent Publication No. 58-107646). According to this process, however, areas in which the patterning direction is not in agreement with the orientation direction of fibrils are readily formed, and often fibrils are cut at unexpected parts in the boundary between the electroconductive zone and insulating zone.
Therefore, as the means for obtaining a good orientation, a process has been proposed in which polyacetylene is drawn in one direction or a magnetic field is applied at the time of synthesis [see, for example, Synthetic Metals, 28 (1989), D51-D56]. Nevertheless, the process in which polyacetylene is drawn is not suitable for the fabrication of devices, and the process for obtaining an orientation by application of a magnetic field is unsatisfactory in that a large apparatus must be used and it is difficult to apply this process to a large substrate.